cohort study

study

cross-sectional study one employing a single point of data collection for each participant or system being studied. It is used for examining phenomena expected to remain static through the period of interest. It contrasts with a longitudinal s.

electrophysiological s's (EPS) studies from within the heart of its electrical activation and response to electrical stimuli and certain drugs. In general they include intravenous and/or intra-arterial placement of one or more electrode catheters at sites in the atria, ventricles, or coronary sinus, and sometimes the pulmonary artery or aorta. They record activity or stimulate the heart at various rates and cadences and are aids in the evaluation of electrophysiologic properties such as automaticity, conduction, and refractoriness. They also initiate and terminate tachycardias, map the sequence of activation, and aid in evaluation of patients for various forms of therapy and for the response to therapy. During these studies catheter ablation procedures, such as radio frequency ablation and electrical ablation, may be performed.

longitudinal study one in which participants, processes, or systems are studied over time, with data being collected at multiple intervals. The two main types are prospective studies and retrospective studies. It contrasts with a cross-sectional s.

pilot study a smaller version of a proposed research study, conducted to refine the methodology of the later one. It should be as similar to the proposed study as possible, using similar subjects, the same setting, and the same techniques of data collection and analysis.

prospective study an epidemiologic study in which the groups of individuals (cohorts) are selected on the bases of factors that are to be examined for possible effects on some outcome. For example, the effect of exposure to a specific risk factor on the eventual development of a particular disease can be studied. The cohorts are then followed over a period of time to determine the incidence rates of the outcomes being studied as they relate to the original factors in question. Called also cohort study.

The term prospective usually implies a cohort selected in the present and followed into the future, but this method can also be applied to existing longitudinal historical data, such as insurance or medical records. A cohort is identified and classified as to exposure to the risk factor at some date in the past and followed up to the present to determine incidence rates. This is called a historical prospective study, prospective study of past data, or retrospective cohort study.

retrospective study an epidemiologic study in which participating individuals are classified as either having some outcome (cases) or lacking it (controls); the outcome may be a specific disease, and the persons' histories are examined for specific factors that might be associated with that outcome. Cases and controls are often matched with respect to certain demographic or other variables but need not be. As compared to prospective studies, retrospective studies suffer from drawbacks: certain important statistics cannot be measured, and large biases may be introduced both in the selection of controls and in the recall of past exposure to risk factors. The advantage of the retrospective study is its small scale, usually short time for completion, and its applicability to rare diseases, which would require study of very large cohorts in prospective studies. See also prospective s.

co·hort stud·y

a study using epidemiologic methods, such as a clinical trial, in which a cohort with a particular attribute (for example, smokers, recipients of a drug) is followed prospectively and compared for some outcome (for example, disease, cure) with another cohort that does not possess that attribute.

cohort study

(in research) a study concerning a specific subpopulation, such as the children born between December and May in 1975 or those born in the same months in 1955. See also prospective study.

cohort study

An observational study in which a defined group of people (a cohort) is followed over time and outcomes are compared in subsets of the cohort who were exposed, not exposed, or exposed at different levels to an intervention or other factor of interest. Cohorts can be assembled in the present and followed into the future (a “concurrent cohort study”), or identified from past records and followed from that time up to the present (a “historical cohort study”). Because random allocation is not used, matching or statistical adjustment must be used to ensure that the comparison groups are as similar as possible.

MADRID -- Patients with knee osteoarthritis who "retreated" into a passive coping strategy and engaged in an unhealthy lifestyle were likely to develop more long-term pain than were patients who stayed physically healthy and emotionally strong, in a large Dutch cohort study.

To investigate the prevalence of urinary incontinence at six months postpartum and study how continence status during pregnancy and mode of delivery influence urinary incontinence at six months postpartum in primiparous women, researchers studied 12 679 primigravid women in the Norwegian Mother and Child Cohort Study, all of whom were continent before pregnancy.

This prospective cohort study used the Swedish Medical Birth Register to collect data on all 763,795 primiparous mothers who had their first births in Sweden between 1987and 2004, with a total of 1,430,464 births.

Appended are: (1) UK Classifications of levels of literacy and numeracy; (2) British Cohort Study 1970--2004 sweep at age 34; (3) Means and Standard errors of the preferred BCS sample (N=3131); and (4) Full specification for Table 2 (main text): The relationship between age 34 basic skills and earnings: men and women.

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